TIGER, a registered trademark of the United States Census Bureau, is a digital database that defines the location and relationship of streets, rivers and other features in the United States to each other. The term TIGER is derived from the acronym Topologically Integrated Geographic Encoding and Referencing. Publicly available TIGER/line files created from the TIGER database include geographic location (latitude/longitude), name and ranges for assigned street addresses for streets/roads in the United States.
Geographic Information System (GIS) software imports TIGER/Line files and uses the information about the relationship between geographic features to produce a map. The map that can be produced from the TIGER/Line files range from a neighborhood street map to a map of the United States.
As the TIGER/Lines files only provide geographical co-ordinates for the endpoints and address ranges for the street segment, the GIS software assumes that each lot or property parcel, that is, each measured parcel of land having fixed boundaries and designated on a plot of survey, on the street segment is the same width. Also, the TIGER/Lines files are only designed to show relative position of elements. Additionally, the address range for a street segment may be incorrect. Thus, the location of the street address may be incorrectly identified blocks from the actual location. The GIS software also assumes that a building on each lot on the street is the same distance from the street/road, and that the building is located in the center of the lot. In campus settings, or with irregular sized or shaped lots this is simply not the case.
However, even with the inaccuracy in location of the street address, the TIGER/Lines file is useful for creating maps that do not require a high level of positional accuracy. For example, a TIGER/Lines file is typically used by applications to provide driving directions between two street addresses or to display the location of property offered for sale.
The TIGER/Lines file can also be used by risk analysis applications. Risk analysis applications are typically used by property insurance underwriters in the insurance industry for generating geographical reports regarding distances from a building to natural hazards such as coastlines, earthquake faults and flood zones.
However, as the source of the much of the data is 1:100,000 scale maps from the United States Geological Survey (USGS) the accuracy is approximately +/−167 feet. Flood zones are irregular and follow a river. Typically, flood risk is determined by whether a building is within 250 feet of a flood plain, thus an error of +/−167 feet in the location of a building is significant.
In the case of a risk management application, the inaccuracies in the database may be critical. For example, the insurance premium is higher if a building is within 250 feet of a flood zone. Thus, the distance from the building to the flood zone is important for both the insurer and the insured. For example, an inaccuracy in position of the building of 50 feet could result in a different, and perhaps significantly higher or lower price for flood insurance. In addition, in the case of a flood claim, the property insurance underwriter that made the incorrect assessment could be liable for the entire value of the building.
Furthermore, the TIGER/Line files do not include every street in the United States. In many cases, this is because a street came into existence after the database was created. Additionally, many street segments are not associated with a name. Thus, the TIGER/Lines files cannot be used by GIS software to locate a street address on an unnamed street.